What is known is that Sandy Hook Elementary School in Connecticut is now the scene of the second-deadliest school shooting in American history. Connecticut police say Adam Lanza, 20, killed his own mother before entering the school grounds with multiple firearms and killing 20 children, six adults and then himself.

What is not known, at least not with certainty, are the reasons why this tragedy happened, why mass shootings seem to be happening with increased frequency and what more can be done to prevent future rampages.

Potential explanations for episodes of mass violence include untreated mental illnesses, relatively easy access to firearms in the United States and even the stress of a weak economy.

Law enforcement has not yet disclosed any motive for the Newtown, Conn., shooting, and an overall explanation for this kind of violence also seems to be elusive.

It is possible that America's police and academics have failed to develop the kind of research strategy to completely understand and prevent rampages, a University of Arizona doctor said.

Dr. John M. Harris, a faculty affiliate at the Tucson university, said he decided to study the phenomenon of mass killings after the January 2011 shooting in that city that killed six and wounded 13 others, including now-retired Rep. Gabrielle Giffords.

Harris said he and his wife considered Giffords a personal friend.

"We started thinking, `Why is this looking like we've seen this before?"' Harris said.

The Tucson incident followed mass shootings that included the November 2009 shooting at Fort Hood, Texas, that resulted in the deaths of 13 soldiers and civilians and the 2007 killings at Virginia Tech University, where 32 died in the worst such incident in American history.

Harris and his wife, Robin, who is an epidemiologist, decided to study the history of mass shootings. They found that despite the attention paid to such events in the United States and around the world, little research has been done that could reveal whether there is a common pathology that motivates rampage shooters, which may help authorities prevent future massacres.

Instead, people tend to respond to events like the Tucson and Newtown shootings by engaging in one-issue arguments that go nowhere, Harris said.

"Let's get off of this as a gun-control issue," he said, "because that gets everybody riled up and we're all yelling at each other."

The Harrises concluded in their article that a better way to comprehend mass violence would be to create a multi-disciplinary research team similar to the National Transportation Safety Board to research rampages and possibly determine methods to help authorities prevent such incidents.

In the short term, however, it appears as if the Newtown shooting will move the debate over gun control to the forefront.

President Barack Obama, in response to the Newtown shooting, called for leaders to take "meaningful action," but did not actually use the words "gun control" during his brief address to the nation on Friday.

California Lt. Gov. Gavin Newsom was more direct:

"For those calling for the postponement of any discussion of gun and mental health policy in America - you are wrong," Newsome said in a statement.

UC Riverside sociologist Robert Nash Parker said a discussion on gun ownership would be appropriate.

Parker, who has previously called for restrictions on sales of "40 ouncers" and other single-servings on alcohol to reduce crime, said the similarly easy access to guns in American society increases the probability of crime.

"In general, the more guns you have available, the more guns you're going to have used," Parker said. "It's not very complicated. It's that politically our society is unwilling to challenge the gun lobby."

Parker's view is the opposite of that of John Lott, author of "More Guns, Less Crime."

Lott said the creation of gun-free zones at schools and other public gathering places has not reduced the probability of gun violence as much as they have given killers easy targets.

In Lott's view, creating places where law-abiding people cannot carry guns for self-defense is a mistake, as is publishing the names of mass murderers.

"It's pretty clear what's happening," he said. "These guys want to commit suicide and they want to do it in a way that will get people to know they existed in life. They know the more people they kill, the more news coverage they will get."

Although there may seem to be a rise in the incidents of mass murders, overall levels of homicide and violent crime have declined in the United States for the past two decades.

The country's murder rate fell from 9.3 per 100,000 residents in 1992 to 4.7 per 100,000 people last year, according to the FBI.

The violent crime rate similarly fell from 757.7 violent incidents per 100,000 Americans to 386.3 violent crimes per 100,000 people in 2011.

"This (the Newtown shooting) is a tragedy of epic proportions. I want to be very hesitant to looking at this as a pattern," said Joshua L. Miller, associate dean for the School for Social Work at Smith College in Massachusetts.